JSON sewer mapgen

[LovamKicsiGazsii]

Summary

Content "Sewer mapgen overhaul"

Purpose of change

Map extras were a rather restrictive way of adding decor to sewers. For one there was no differentiation between curved, straight or fourway sewer tiles which prevented me from adding walls. Same goes for pipes and walkways; how I attempted to solve it was branch them out in all directions, hoping that they'd connect with a neighboring tile. The technique started show its faults after a while.

Fixes #58404 (I hope)
Partially addresses #62747

Describe the solution

Removed sewer map extras and replaced them with regular JSON mapgen. These maps take sewer shape into account, making connected walls, pipes and walkways possible. As an added bonus, this also frees up slots for new sewer extras.

I also edited locations with sewer accesses to have a seamless connection with the new design.
Dehardcoded manhole ladder placements for the extra flexibility.

Describe alternatives you've considered

Removing hardcoded mapgen. Not sure how to do that.

Testing

Auto-walked through what felt like 500 map tiles of sewers. I also checked individual variants by inflating their weights and guaranteeing nested chunk placements.

Additional context

Screenshots:

[NetSysFire]

As the author of #58404, yes this fixes it. Very nice work!